JP5475760B2 - System and method for supporting multi-user antenna beamforming in a cellular network - Google Patents

Description

Related Application Data This application is related to provisional patent application No. 61/075215 filed on June 24, 2008. S. C. Claim priority to this earlier application under §119 (e). This provisional patent application is incorporated by reference into this patent application.

  The present invention relates to supporting signal power fluctuations for spatial beams for multiple users in a cell segment.

  There is an increasing demand for mobile wireless operators to provide voice and high-speed data services, while these operators reduce overall network costs and make services affordable for subscribers. It is hoped that more users will be supported per base station. As a result, there is a need for a wireless system that allows higher data transfer rates and increased capacity. The spectrum available for wireless services is limited, and previous attempts to increase traffic within a fixed bandwidth have increased interference in the system and reduced signal quality.

  A wireless communication network is typically divided into cells, and each cell is further divided into cell sectors. A base station is provided in each cell, and wireless communication with a mobile station located in the cell becomes possible. One problem exists when prior art omnidirectional antennas are used in base stations. This is because the transmission / reception of each user's signal becomes a source of interference for other users located within the same cell location on the network, limiting the overall system interference. Such an omnidirectional antenna is shown in FIG.

  In these conventional omnidirectional antenna cellular network systems, the base station has no information about the location of the mobile unit in the cell and radiates signals in all directions in the cell to provide radio coverage. To do. As a result, in addition to causing interference for neighboring cells using the same frequency, so-called co-channel cells, power during transmission is wasted when there are no mobile units to reach. Similarly, for reception, the antenna receives signals coming from all directions, including noise and interference.

  An effective way to improve the efficiency of bandwidth usage and reduce this type of interference is to use multiple input multiple output (MIMO) technology that supports multiple antennas at the transmitter and receiver. . For multi-antenna broadcast channels such as downlink on cellular networks, cells are divided into multiple sectors and sectored antennas are used to simultaneously communicate with multiple users to maximize downlink throughput Transmission / reception methods have been developed. Such sectored antenna technology provides a significantly improved solution to reduce interference levels and improve system capacity.

  A sectored antenna system is characterized by a central transmitter (cell site / tower) that communicates simultaneously with multiple receivers (user equipment, cell phones, etc.) involved in a communication session. In this technique, each user's signal is transmitted and received by the base station only in the direction of that particular user. This allows the system to significantly reduce overall interference within the system. The sectored antenna system shown in FIG. 1 (b) consists of an array of antennas that send different transmit / receive beams for each user located within the coverage area of the sector of the cell.

  In order to improve the performance of the sectorized cell sector, a scheme has been implemented that uses an Orthogonal Frequency Domain Multiple Access (OFDMA) system, also called a Space Division Multiple Access (SDMA) system. In such a system, a mobile station can communicate with a base station using one or more of these spatial beams. This method, called beamforming, is made possible by advanced signal processing at the base station, which directs transmission and reception of signals to be orthogonal (orthogonally directing transmission and reception of signals).

  A beamforming scheme is defined by the formation of multiple spatial beams within a cell sector to divide the cell sector into different coverage areas. The radiation pattern of the base station is adapted so that each user gets the highest gain in the direction of that user, both for transmission and reception. A communication technique called Spatial Division Multiple Access (SDMA) has been developed to improve performance by using sectored antenna technology and by taking advantage of the spatial location and channel characteristics of mobile units within the cell. . Spatial division multiple access (SDMA) techniques essentially create multiple uncorrelated spatial pipes that are transmitted simultaneously by beamforming and / or precoding, thereby enabling multiple access wireless communication systems. Excellent performance can be provided.

  One type of beamforming scheme is an adaptive beamforming scheme that dynamically directs the beam to the location of the mobile station. Such adaptive beamforming schemes require mobility tracking that tracks the location and spatial characteristics of the mobile station to generate an adaptive beam. Depending on the location and spatial characteristics, each user's signal is multiplied by a complex weight that adjusts the signal to each antenna and the magnitude and phase of the signal from each antenna. This allows the output from the array of sectorized antennas to form a transmit / receive beam in the desired direction, while minimizing the output in the other direction, which can be seen schematically in FIG. Precoding is an implementation of beamforming that uses a given codeword, where each codeword is a set of weights for antenna elements.

  In order to support communication for user equipment, the user equipment may instruct about output signal values or signal levels that need to be set for transmission to the user equipment, especially when multiple users are located on a cell site. Receive. In the prior art, user equipments 205 and 210 are per resource element via Radio Resource Control (RRC) signaling as shown in the initial release of the 3GPP TS 36.213 standard (eg TS 36.213 v8.3.0). Directed on energy allocation per resource element (EPRE) output level. However, due to the dynamic nature of scheduling, it has been found that power level RRC signaling is too slow to follow the rapid fluctuations in power level encountered on the system. This problem results in performance loss because users on a multi-user MIMO system may change at a rate higher than the frequency of RRC signaling. Furthermore, specifying power levels for user equipment using RRC signaling has other drawbacks, including increased scheduler complexity and the need for more power level RRC signaling.

  Currently known methods of commanding user equipment for energy allocation per resource element (EPRE), which is a signal strength value or signal strength level for transmission to the user equipment, is the output produced by dynamic scheduling of transmissions on the cell site. It is not fast enough to keep up with rapid fluctuations in level, so that multiple users located on the same cell site can be scheduled for transmission using the same channel resources In particular, there is a need for improved signal strength signaling or signal level signaling for user equipment. There is also a need for support for sectorized beamforming antenna systems in multi-user mobile broadband communication networks, including solving the problems identified above.

  Depending on the terminology used on a particular network configuration or communication system, various components on the system may be referred to by different names. For example, “user equipment” may be a variety of PCs on cable networks and mobile terminals (“cell phones”) having various features and functions such as Internet access, email, messaging services, etc. Includes other types of devices that can be experienced in configurations and models, directly coupled to the cellular network through wireless connectivity.

  Furthermore, the terms “receiver” and “transmitter” are referred to as “access point (AP)”, “base station”, and “user”, depending on which direction communications are being transmitted and received. Sometimes. For example, in a downlink environment, an access point AP or base station (eNodeB or eNB) is a transmitter and a user is a receiver, whereas in an uplink environment, an access point AP or base station (eNodeB Or eNB) is a receiver and the user is a transmitter. These terms (such as transmitters and receivers) are not meant to be limitingly defined and can include various mobile communication units or transmission devices located on the network.

  The present invention is a method and system for supporting a beamforming antenna system in a multi-user mobile broadband communication network that includes the process of setting and adjusting the magnitude and phase of the signal from each antenna to the user equipment. That is, the present invention supports communication of output signal values or output signal levels to user equipment in a manner that follows the rapid fluctuations in power levels that occur with dynamic scheduling of transmissions on cell sites. The present invention fulfills this need for improved signal strength signaling to user equipment for situations where multiple users are located on a cell site.

  Objects and features of the present invention will be more readily understood from the following detailed description and appended claims when read with the accompanying drawings in which like numerals represent like elements.

FIG. 2 is a diagram of an omnidirectional antenna (a) and a sectorized antenna (b). FIG. 2 is a diagram of a weighted sectorized transmission beam directed to a desired user. FIG. 2 is a block diagram of exemplary components of a base station and a mobile station.

  In FIG. 1 (a), the overall transmission architecture 100 of the omnidirectional antenna 105 transmitting equally radially outwardly in the various directions indicated by arrows 125, 115, 135, and 140. The perimeter of the coverage area is indicated by area 120 for transmission architecture 100. By using the sectored antenna architecture 141 shown in FIG. 1 (b), an efficiency improvement has been achieved.

  A plurality of antennas 145, 147, and 148 are shown in architecture 140, each antenna being directional transmission 175 for coverage area 150, transmission 190 for coverage area 157, and directional transmission for coverage area 155. Directed to a different area of the cellular network, indicated at 180. In this situation, it is possible to improve system capacity with a sectored architecture.

  By varying the strength of the various transmitted signals, additional efficiency and interference reduction can be achieved, as shown in FIG. Multiple antennas 215, 220, 227, and 230 send (or receive) transmissions within the sectored antenna architecture 200. A directional antenna beam 235 is formed by increasing the strength of that signal from the antenna element 230. A desired user 205 is shown receiving a desired transmission 245 within a high signal strength coverage area 235, and the desired transmission 245 is a higher power beam intended to be directed to that user 205. is there. An interfering user 210 is shown with a lower strength transmission signal 240, and the lower strength transmission signal 240 reduces the interference experienced by the system associated with that user 210.

  According to some preferred embodiments, “opportunistic” space-time multiple access (OSTMA) techniques are provided for use in wireless communication networks. The Ostma technique allows the formation of multiple spatial beams in a cell segment (cell or cell sector), wherein at least some of the multiple spatial beams of the cell segment are associated with different power levels, Different coverage areas are provided. A spatial beam (or, more simply, a “beam”) is a geographically distinct within a cell segment in which wireless communication between a base station and mobile station (s) can be performed. Refers to the coverage area.

  An OSTMA scheme is provided for the forward wireless link from the base station to the mobile station. In an alternative embodiment, the OSTMA scheme may be used for the reverse wireless link from the mobile station to the base station. The communication connection through which data flows from the base station to the mobile station is called the forward link (FL). Similarly, a communication connection in which data flows from a mobile station to a base station is called a reverse link (RL). Communication conditions are not always the same for both FL and RL. For example, a mobile station [mobile station] may be communicating with a serving base station [serving base station] that has highly congested [highly congested] RL traffic but a relatively open FL flow. . The mobile station may need to adjust its RL connection. Staying at the same base station for both FL and RL (if a more open RL connection is available from another base station) may not be the best use of communication resources.

  Exemplary components in the preferred embodiment include base station 1000 and mobile station 1002 shown in FIG. Base station 1000 includes a wireless interface 1004 that communicates wirelessly with a wireless interface 1006 within mobile station 1002 via a wireless link. Base station 1000 includes software 1008 that is executable on one or more central processing units (CPUs) 1010 within base station 1000 to perform base station tasks. CPU (s) 1010 is connected to memory 1012. Software 1008 may include a scheduler and other software modules. Base station 1000 also includes an inter-base station interface 1014 for communicating information such as backhaul information and / or coordination information with another base station.

  Similarly, mobile station 1002 includes software 1016 that is executable on one or more CPUs 1018 connected to memory 1020. Software 1016 can be executed to perform the tasks of mobile station 1002. Such software (1008 and 1016) instructions may be loaded for execution on a CPU or other type of processor. The processor can include a microprocessor, microcontroller, processor module or subsystem (including one or more microprocessors or microcontrollers), or other control or computing device. A “processor” can refer to a single component or multiple components.

  Data (in software) and instructions are stored in respective storage devices, which are implemented as one or more computer-readable storage media or computer-usable storage media. Storage media include dynamic or static random access memory (DRAM or SRAM), erasable and programmable read only memory (EPROM), electrically erasable and programmable read only memory (ERPROM), flash memory, etc. Various, including semiconductor memory devices, fixed disks, floppy disks, removable disks such as removable disks, other magnetic media including tapes, optical media such as compact disks (CDs) and digital video disks (DVDs) In the form of memory.

  When multiple users 205 and 210 as shown on FIG. 2 are serviced on the same cell site sector, the signal output from the transmit antenna 230 must be divided among these multiple users. I must. A user 205 or 210 in multi-user MIMO mode can have one of several values for the user's EPRE power level, depending on the number of users simultaneously served on that cell site sector. You should expect to have sex.

  In the prior art, user equipments 205 and 210 are configured with EPRE power levels via Radio Resource Control (RRC) signaling as shown in the initial release of the 3GPP TS 36.213 standard (eg TS 36.213 v8.3.0). Get a directive on. However, due to the dynamic nature of scheduling, it has been found that power level RRC signaling is too slow to follow the rapid fluctuations in power level encountered on the system. This problem results in a loss of performance because users on a multi-user MIMO system may change at a rate higher than the frequency of RRC signaling. Furthermore, specifying power levels for user equipment using RRC signaling has other drawbacks, including increased scheduler complexity and the need for more power level RRC signaling.

  The present invention solves the problems associated with power level RRC signaling by providing power level information to the user equipment 205 or 210 via bits specified in the scheduling message for users in multi-user MIMO mode. Advantages of communicating power level information using scheduling messages instead of RRC signaling include full scheduler flexibility, improved performance, and reduced need for RRC signaling for scaling factor updates. . Furthermore, since the signal-to-noise ratio for multi-user MIMO users tends to be quite high, the increase in control channel overhead (as a percentage of achievable throughput) to include power level information in the Grant message is significant. Get smaller.

  The present invention uses several bits in a scheduling message sent from base station 1000 to users 205 and 210 (or mobile station 1002). The Scheduling Grant message can be said to be related to the Physical Downlink Shared Channel (PDSCH) transmission mode identified in the signaling format for multi-user MIMO transmission. The present invention merges the multi-user MIMO mode and the closed-loop Rank-1 precoding transmission mode as a single designated mode with transmit antenna designation bits. This is because the closed-loop precoding transmission mode is a subset of the multi-user MIMO mode. That is, the present invention does not require higher layer RRC signaling that is required in the prior art to change from one transmission mode to another transmission mode, via multi-user MIMO via a designated bit in the scheduling message. And dynamic switching between closed-loop Rank-1 and Rank-2 precoding transmissions. By using the designation bits in the scheduling message sent to the user, the present invention combines two separate transmission mode designations as a single transmission mode designation, so that the control message's Overhead is reduced and transmission mode designation in the system is simplified.

  In the present invention, when an eNodeB is transmitting to multiple user equipments such as 205 and 210 in FIG. 2, the eNodeB must divide the output between the different user equipments. The amount of power splitting depends on the number of user equipment that must be serviced on the cell segment using the same channel resource. For example, when two user devices are receiving service, the output split for user device 205 is specified in the precoding table [1 1 1 1] / sqrt (2), and the output split for user device 210 is pre- It is specified by the coding table [1 -1 1 -1] / sqrt (2). However, 1 / sqrt (2) is used as a scaling factor for the two precoders that reduce the output signal being transmitted to each user equipment. If 4 transmitter antenna systems are supported on the eNodeB, for N users scheduled for the same channel resource, the precoder will precode the table [precoding table] [1 1 1 1] / sqrt. (N) can be used to scale the power level for user equipment 205, and other signals for other user equipment are specified in a predetermined precoding table assigned to such other user equipment. Reduced by a proportional factor.

  In the present invention, the scaling factor is signaled to the user equipment using an additional designated bit in the message sent to the user equipment. In one embodiment, additional bits can be added to a new format message (eg, Format 1B), or from specified bits of an existing message format (eg, Format 2 for a user in a multi-user MIMO Grant message). The specified bit can be reinterpreted. If there are only two transmitters since there are one to two users on the cell segment, only one additional designation bit in the format message is required. If there are a maximum of 4 users on the cell segment and therefore 4 transmitters are required, then 2 additional designated bits are required in the format message.

When the user equipment 205 receives the bit designation in the format message, the user equipment 205 applies the scaling factor to be applied to the power level for that user equipment based on the number of transmitter antennas and number of users specified by the designated bit. Calculate The output scaling factors P_A and P_B can be determined by the user in this manner, and the output scaling factor can be used at the receiver to demodulate the received signal. The system dynamically adjusts the output of the transmitted signal in a very fast manner using the designated bits, and the user demodulates the signal at the receiver using a scaling factor. The user equipment may use -10 log ₁₀ N with N = 1, 2 for 2 transmitter antenna bit designations using 1 bit, or N = 1, 2, for 4 transmitter antenna bit designations with 2 bits. Scaling factors P_A and P_B may be calculated using a predetermined scaling factor such as 3, 4 −10 log ₁₀ N, or a value from a precoding table. This embodiment can be used with a new format message (eg, Format 1B) or reinterpret the specified bits from the specified bits of an existing message format (eg, Format 2 for users in a multi-user MIMO Grant message) can do. Alternatively, the designated bits can be used to look up the scaling factor from a precoding lookup table or other table resource on the system.

Alternatively, the bit designation in the format message can provide the user equipment with the actual scaling values P_A and P_B, which uses more bits than the traditional designation method, but the user equipment uses P_A And eliminates the computation of the P_B scaling value, allowing for faster protocol processing. The actual value of the P_A and P_B scaling values can be specified with designated bits, or can be defined in a table or represent a predetermined factor known in the system. For example, 3 bits specifying P_A can define the dB value (eg, dB = 3, 2, 1, 0, −1, −2, −3, −6) to be applied to the output related to signal strength. , A specified bit can define a table entry in a specified scaling table (eg, 3 bits specify an entry on a scaling table or precoding table) or known to the system The scaling factor is P_A = -10 log ₁₀ N with N = 1, 2 for 2 transmitter antenna bit designations, or P_A = -10 log with N = 1, 2, 3, 4 for 4 transmitter antenna bit designations ₁₀ N is specified. The output scaling factors P_A and P_B can be determined by the user in this manner, and the output scaling factor can be used at the receiver to demodulate the received signal. The system dynamically adjusts the output of the transmitted signal in a very fast manner using the designated bits, and the user demodulates the signal at the receiver using a scaling factor. This embodiment can be used with a new format message (eg, Format 1B) or reinterpret the specified bits from the specified bits of an existing message format (eg, Format 2 for users in a multi-user MIMO Grant message) can do.

  In the above description, numerous details are set forth to provide an understanding of the present invention. However, those skilled in the art will appreciate that the invention may be practiced without such details. While the invention has been disclosed with respect to a limited number of embodiments, those skilled in the art will appreciate numerous modifications and variations thereof. The appended claims are intended to cover modifications and variations that fall within the true spirit and scope of the invention.

Claims (22)

A method for specifying an output scaling factor for a transmission beam from an access node to a receiver on a communication system having at least two spatial beams that achieves coverage within a cell sector, comprising:
Determining at the access node the output scaling factor to be used to apply to the transmitted signal to one of the receivers, the output scaling factor being the same as the resource allocation on the network Required based on the number of receivers communicated via
Preparing a designated bit format message at the access node based on the output scaling factor determined at the access node;
Periodically transmitting the designated bit format message from an access node via one or more spatial beam transmissions, wherein the designated bit included in the designated bit format message is received by the receiver; Used to calculate the output scaling factor for the transmission beam to the receiver and dynamically adjust the output of the transmission signal to the receiver based on the output scaling factor. The transmitted signal is demodulated at the receiver using the output scaling factor calculated from the designated bit format message. If because there are two users from one on the cell segment requires two transmitters, the designated bit format message, one additional designation bit of the specified bit format message The method of claim 1, wherein: If because there are four users at a maximum on the cell segment requires four transmitters, the designated bit format message, two additional designation bit of the specified bit format message The method of claim 1 in need. The output scaling factor is calculated using the equation -10 log 10N for N = 1, 2 for two transmitter antenna bit designations that use one bit in the designated bit format message. the method of. The output scaling factor is calculated using the equation −10 log 10 N as N = 1, 2, 3, 4 for 4 transmitter antenna bit designations using 2 bits in the designated bit format message. Item 2. The method according to Item 1. The method of claim 1, wherein the output scaling factor is calculated using a value specification from a table of predetermined values in the communication system. A method for specifying an output scaling factor for a transmission beam from an access node to a receiver on a communication system having at least two spatial beams that achieves coverage within a cell sector, comprising:
Determining at the access node the output scaling factor to be used to apply to the transmitted signal to one of the receivers, the output scaling factor being the same as the resource allocation on the network A value adjustment for the transmission beam based on the number of receivers communicated through the resources of
Preparing a designated bit format message at the access node based on the output scaling factor determined at the access node;
Periodically transmitting the designated bit format message from an access node via one or more spatial beam transmissions, wherein the designated bit included in the designated bit format message is received by the receiver; Specifying an actual value of the output scaling factor for the transmission beam to the receiver, and dynamically adjusting the output of the transmission signal to the receiver based on the output scaling factor The transmission signal being demodulated at the receiver using the output scaling factor calculated from the designated bit format message.   The method according to claim 7, wherein the designated bit format message specifies a dB [dB rating] rate to be applied to the transmission signal. The method of claim 7, wherein the specified bit format message specifies an actual value from a table of predetermined values in the communication system. The designation bit format message, the second transmitter antenna bit designation using one bit in the designated bit format message, the actual power scaling value using Equation -10log10N as N = 1, 2 The method of claim 7 wherein: The output scaling factor is calculated using the equation −10 log 10 N as N = 1, 2, 3, 4 for 4 transmitter antenna bit designations using 2 bits in the designated bit format message. Item 8. The method according to Item 7. A transmission system for specifying an output scaling factor for a transmission beam from an access node to a receiver on a communication system having at least two spatial beams that achieves coverage within a cell sector, comprising:
The output scaling factor to be applied to the transmission beam to the receiver is determined based on the resource allocation on the network and the number of receivers communicated through the same resource, and is specified based on the output scaling factor An access node comprising a processor for preparing a bit format message and a transmitter for periodically transmitting a specified bit format message via one or more spatial beam transmissions, the specified bit An access node in which a format message is used at the receiver and an output scaling factor for the transmission beam to the receiver is calculated;
The access node dynamically adjusts the output of the transmission signal to the receiver based on the output scaling factor without creating interference with other transmissions on the network, the transmission signal comprising: A transmission system demodulated at the receiver using the output scaling factor received from the access node. If because there are two users from one on the cell segment requires two transmitters, the designated bit format message, one additional designation bit of the specified bit format message The system of claim 12, wherein: If because there are four users at a maximum on the cell segment requires four transmitters, the designated bit format message, two additional designation bit of the specified bit format message The system of claim 12 in need. 13. The output scaling factor is calculated using the equation −10log10N with N = 1, 2 for two transmitter antenna bit designations that use one bit in the designated bit format message. System. The output scaling factor is calculated using the equation −10 log 10 N as N = 1, 2, 3, 4 for 4 transmitter antenna bit designations using 2 bits in the designated bit format message. Item 13. The system according to Item 12.   The system of claim 12, wherein the output scaling factor is calculated using a value specification from a table of predetermined values in the system. A transmission system for specifying an output scaling factor for a transmission beam from an access node to a receiver on a communication system having at least two spatial beams that achieves coverage within a cell sector, comprising:
Determining the output scaling factor, which is an actual value adjustment to be applied to the transmission beam to the receiver, based on resource allocation on the network and the number of receivers communicated over the same resource, and the output An access node having a processor that prepares a specified bit format message based on a scaling factor and a transmitter that periodically transmits the specified bit format message via one or more spatial beam transmissions. The designated bit format message comprises an access node designating an actual value of the output scaling factor for the receiver with respect to the transmission beam to the receiver;
The access node dynamically adjusts the output of the transmission signal to the receiver based on the output scaling factor without creating interference with other transmissions on the network, the transmission signal comprising: A transmission system demodulated at the receiver using the output scaling factor received from the access node. The system of claim 18 , wherein the designated bit format message specifies a dB rate to be applied to the transmitted signal. The system of claim 18 , wherein the designated bit format message specifies an actual value from a table of predetermined values in the communication system. The designation bit format message, the second transmitter antenna bit designation using one bit in the designated bit format message, the actual power scaling value using Equation -10log10N as N = 1, 2 The system of claim 18 , wherein: The output scaling factor is calculated using the equation −10 log 10 N as N = 1, 2, 3, 4 for 4 transmitter antenna bit designations using 2 bits in the designated bit format message. Item 19. The system according to Item 18 .

Images